This invention relates to a primer composition, and more particularly, to a primer composition of gamma-aminopropyltrimethoxy silane and to the use of a primer composition for promoting adhesion of condensation cure silicones in the cured state to substrates.
Silane coupling agents have been used in the prior art to promote the adhesion of various silicone materials and various organic adhesives and polymers, such as epoxy resins, polyurethane resins, and the like to a variety of substrates as explained in U.S. Pat. Nos. 4,921,880 and 4,927,953 which are incorporated by reference herein in their entirety. In U.S. Pat. No. 4,921,880, it is indicated that even though silanes and certain other silicon containing compounds function as coupling agents and adhesion promoters, they do not function equally in all situations, and the usefulness thereof depends on the type of substrate, the type of material being bonded to the substrate and the conditions under which the adhesive bond is to perform. According to U.S. Pat. No. 4,921,880, the silane coupling agents are those which have organofunctional groups bonded to the silicon atom, such as a vinyl functional, vinyl or methacrylate groups, as well as hydrolyzable groups, such as methoxy or ethoxy groups bonded to the silicon atom. In U.S. Pat. No. 4,927,953, gamma-aminopropylalkoxy silanes are described as silane coupling agents which increase the mechanical strength of the organic polymer bonded with an inorganic material.
In coupling the inorganic materials of substrates to organic adhesives or coating compositions with alkoxysilylpropylamine coupling agents, it appears that the alkoxy groups on the silane of the alkoxysilylpropylamines condense with pendant hydroxy groups on the surface of the inorganic material (and with the hydroxy groups in water from atmospheric moisture), and the reactive aminopropyl group of the molecule is presented to the organic adhesive or coating material, such as the epoxy, where it is available for covalent bonding, and forms a covalent bond therewith. Theory of the formation of silane bonds with polymers is described at pages 42 and 128 of the book entitled "Silane Coupling Agents" published by Plenum Press in 1982. At pages 134-136 of the book entitled "Silane Coupling Agents", there is a discussion of the silane bonds formed with polymers and of bonding through interpenetrating networks and the strengthening of boundary layers. It is indicated that a major function of adhesion promoters is to strengthen the boundary layer whether the adhesion promoter is applied as a primer or used as an integral additive.
In U.S. Pat. No. 2,832,754, trialkoxysilylpropylamines are proposed as a size or finish for fibrous glass materials prior to the preparation of reinforced plastics, and according to U.S. Pat. No. 2,832,754, laminates prepared from reinforced plastics having fibrous glass materials treated with trialkoxysilylpropylamines have a superior glass to resin bond when used in such thermosetting resins as aldehyde condensation resins, epoxy resins and urethane resins. According to U.S. Pat. No. 2,832,274, which is incorporated by reference herein in its entirety, because the trialkoxysilylpropylamines form stable solutions with aqueous organic admixtures or with water, they can be used to size or finish fibrous materials without employing anhydrous organic solvents.
Aminopropyltrialkoxy silanes have been used alone and in combination with various other silanes as priming agents in the prior art where they have been applied with various organic solvents. In U.S. Pat. No. 3,022,196, which is incorporated herein by reference in its entirety, aminopropyl silanes containing three --OR groups (alkoxy groups) with aminopropyltriethoxysilane being the preferred silane, are mixed with alkyltrialkoxy silanes and applied to a solid body when dissolved in any solvent for the components which solvent is also miscible with water, for example, alcohols, glycols, ketones, glycol ethers, and the like. The priming agents of U.S. Pat. No. 3,022,196 may be used to bond silicone rubber to a wide variety of solid bodies of the type used in making structural fabrications including metal, ceramic, glass, wood, resins, resin-bonded bodies, rubber, hydraulic cement, textiles containing synthetic organic fibers and the like. In U.S. Pat. No. 3,445,326, which is incorporated herein by reference in its entirety, amino-substituted silanes, such as gamma-aminopropyltriethoxysilane, is applied to a thin, flexible, non-porous substrate or structure, such as aluminum foil or flexible plastic film, and dried, prior to applying a thin film of non-porous coating material, such as polypropylene or polyethylene film, thereon. Non-porous films suggested as substrates in U.S Pat. No. 3,445,326 include Mylar.RTM., saran-coated cellophane, nitrocellulose-coated cellophane and cellophane, and the primers may be applied thereto from solution in any of many organic solvents, including hydrocarbon solvents, or in aqueous solution or aqueous dispersion. In U.S. Pat. No. 4,233,428, primer compositions containing gamma-aminopropyltrimethoxylsilane are applied to porous substrates, e.g., mortar and concrete, prior to applying silicone rubber curable at room temperature, thereto.
In U.S. Pat. No. 3,477,901, which is incorporated by reference herein in its entirety, silanes having a general formula which includes aminopropyltrimethoxysilane, mixed with monocarboxylic acids o r silanes which include alkyltrialkoxy silanes, are used to adhere a polyolefin to a substrate when in a liquid form including a solvent solution. In U.S. Pat. No. 3,477,901, any solvent can be employed that has no deleterious effect on the substrate or composition, including such solvents as methyl alcohol, ethyl alcohol, propyl alcohol, hexane, heptane, naphtha mineral spirits, Stoddard solvent, toluene, perchloroethylene and water. In U.S. Pat. No. 3,665,027, which is incorporated by reference herein in its entirety and which relates to a process for preparing gamma-aminopropylalkoxysilanes, silanes are used in the surface treatment of textiles, leather, ceramics and glass for corrosion protection of metals, as primer and adhesive, as well as for modifying synthetics.
Various methods of preparing aminopropyltrialkoxysilanes, including gamma-aminopropyltrimethoxysilane, are described in U.S. Pat. Nos. 4,045,460; 4,481,364; 4,556,722; 4,921,988 and 4,927,949, all of which are incorporated by reference herein in their entirety. In general, these references teach that the aminopropyltrialkoxysilanes are used as adhesion promoters or as coupling agents for various materials including inorganic materials, such as glass fibers, and organic polymers, such as vinyl plastisols, polyurethane elastomers, epoxy- and acrylic-based inks, and the like. In U.S. Pat. No. 4,927,949, the use of a solvent for the preparation of the aminoalkylalkoxysilane is not particularly required, but a solvent may be used to increase the solubility of the special rhodium catalyst or to help control the reaction temperature. Examples of such a solvent in U.S. Pat. No. 4,927,949 include hydrocarbon-type solvents, such as toluene, xylene, cyclohexane, and the like; halogenated hydrocarbon-type solvents, such as chloroform, carbon tetrachloride, and the like; ether-type solvents, such as ethylether and the like; ester-type solvents such as, ethyl acetate and the like; ketone-type solvents, such as acetone and the like; as well as aprotic polar solvents, such as dimethylformamide and dimethylacetamide. However, these solvents are used at the time of the reaction in the preparation of the aminoalkylalkoxysilane when it is prepared from the hydrosilylation of an allylamine with an alkoxyhydrosilane in the presence of a rhodium complex catalyst having a heterocyclic compound containing nitrogen and/or sulfur atoms as a ligand, and they are not present in the final product.
In U.S. Pat. No. 4,052,524, which is incorporated by reference herein in its entirety, it is suggested that gamma-aminopropyltrimethoxysilane is used in water (an aqueous system) for steel to improve adhesive bonding of rubber to steel for steel belted tires. In U.S. Pat. Nos. 4,921,880; 4,921,988; 4,927,953, all of which are incorporated by reference herein in their entirety, silane coupling agents and their use to enhance the adhesion of a variety of organic and silicone compositions to substrates, are disclosed.
In many commercial methods of priming a surface, it is necessary to abrade the surface prior to application of the primer thereto. Abrasion of surfaces is labor intensive, and in most instances abrasion is unevenly applied to the surface. Abrasion of films, e.g., polyimide films which have a low propagation tear strength, often results in scratches on the film which can act as sites of tear initiation. In those cases when the film is loaded with (contains) carbon, abrasion of the surface will generate conductive particles on the surface. Furthermore, the black carbon particles will degrade the optical properties of white coating material (paint) applied to the abraded surface if the carbon particles are not fully cleaned from the surface. Accordingly, it is desirable to find alternatives to primer methods, systems and compositions which require abrasion of the surfaces prior to application of a primer thereto.
Although it is well-known in the prior art that the aminoalkylalkoxysilanes, in general, and that gamma-amino-propyltrimethoxysilane, specifically, can be used as an adhesion promoter when applied as a primer composition to both porous and non-porous substrates, it is desirable to improve such primer compositions. Furthermore, it is desirable to improve the adhesion of coating materials not only to abraded substrates, but also to unabraded substrates. It is especially desirable to improve the adhesion of coating compositions, for example, certain condensation curable, polymerizable organosiloxanes, to unabraded, non-porous resin substrates, for example, to polyimide film. It is also desirable to improve coated articles made from flexible or non-flexible, porous or non-porous substrates by improving the adhesion of the coating materials to the substrates.